The present invention relates to an OAM detecting apparatus and an OAM detecting method for use with an asynchronous transfer mode (ATM) network using an asynchronous transfer mode for detecting an OAM cell in an ATM layer.
For supervisory control of a network on an ATM layer, the internal standards such as ITU-T stipulate an alarm transfer method using an OAM cell called xe2x80x9calarm indication signal (AIS) cellxe2x80x9d or xe2x80x9cremote defect indication (RDI) cell. In the ATM network including exchanges, an exchange having detected a line failure transmits one AIS cell per second in an upstream direction. Devices on the upstream sides receive the AIS cell to recognize that the line has been failed. In this situation, the devices recognize that the failed state of the line is already removed when the AIS cell is not received for a period of 2.5 seconds (xc2x10.5 second). On the other hand, when an exchange on the upstream side detects an AIS cell, the exchange sends one RDI cell per second in a downstream direction. Devices on the upstream sides receive the RDI cell and recognize that the line has been failed. When the RDI cell is not received 2.5 seconds (xc2x10.5 second), the devices recognize that the line failure is already restored.
The ATM layer has a sublayer called xe2x80x9cvirtual path levelxe2x80x9d which handles an OAM cell referred to as xe2x80x9cVP-AIS cellxe2x80x9d or xe2x80x9cVP-RDI cellxe2x80x9d. The ATM layer includes another sublayer, i.e., virtual channel level at which an OAM cell called xe2x80x9cVC-AIS cellxe2x80x9d or xe2x80x9cVC-RDI cellxe2x80x9d is used. Discussion has been fully conducted for an alarm transfer method using the OAM cell in a system in which one station is connected to one station. However, it is required to further discuss a system in which one station is linked to a plurality of stations.
From the standpoint of traffic supervisory control, Japanese Patent Publication No. 2806862 describes a prior art employing a policing function. As can be seen from FIG. 6, this article describes a cell traffic supervisory control system. The system includes a cell detector 101 to detect a valid cell and an invalid cell of ATM cells received and to identify a VPI/VCI number, a timer counter 102, a memory cyclic unit 103, an arithmetic unit 104, a memory 105, a comparator 106, and a discarding unit 107. Timer counter 102 generates, at a timing synchronized with a cell synchronous signal, an arrival time of an ATM cell and a point of time at which memory cyclic unit 103 patrolled memory 105. Memory 105 stores for each VPI/VCI number various parameter data including an arrival time of a previous cell, a bucket counter value, a cell interval time, and a traffic threshold value. Arithmetic unit 104 calculates a bucket counter value according to a current cell arrival time, a patrol time of memory 105, and various parameter data stored for each VPI/VCI number in memory 105. Memory cyclic unit 103 updates the previous cell arrival time and the bucket counter value stored for each VPI/VCI number in memory 105 before an interval of time between the current cell arrival time of an ATM received and the previous cell arrival time of a previous cell equal in the VPI/VCI number to the current cell exceeds a predetermined limit value of timer counter 102. Comparator 106 compares the bucket counter value attained by an arithmetic unit 104 with a traffic threshold value held in memory 105. Discarding unit 107 discards the received ATM cell when the cell is recognized as an illegal or invalid cell as a result of the comparison.
When it is desired to implement an alarm transfer system using an OAM cell in an ATM network in which one station is connected to a plurality of stations, there arises a problem that a large number of RDI cells are returned from an upstream direction, which adversely influences normal lines depending on cases.
For example, as can be seen from FIGS. 2 and 7, in a system in which one station is connected to a plurality of stations (FIG. 2), when a failure occurs between station A (a leaf station) and station B (a repeater station), one AIS cell is sent per second in a reverse direction. When the AIS cell is received by stations E, F, G and H (root stations), each station returns an RDI cell. Resultantly, stations A and B each receive four RDI cells per second. In consequence, if the system includes n root stations, each of stations A and B will receive n cells per second. This means that the number of RDI cells to be received considerably increases as the number of root stations becomes greater. This adversely influences normal connections depending on cases.
Moreover, when a double failure occurs in an ATM network in which one station is connected to a plurality of stations, two kinds of failed position display information items are received at the same time. This possibly leads to a problem that failed positions cannot be correctly determined. For example, as shown in FIGS. 4 and 8 in which connections are established between one station and a plurality of stations, when a fault takes place between station C (repeater station) and station E (root station) as well as between station D (repeater station) and station H (root station), stations C and D each transmit an AIS cell in a forward direction (upstream to downstream). Since failed position (breakdown position) display information varies between stations C and D, the AIS cells from stations C and D are different from each other. Station A therefore receives the AIS cells including failed position display information of two different types respectively from stations C and D at the same time and hence cannot appropriately determine the failed positions. Stations A to H which determine failed positions according to RDI cells also receive two kinds of failed position display information. Consequently, it is also impossible for stations A to H to correctly determine the failed positions.
In a cell traffic supervisory control system of the prior art shown in FIG. 6, a large number of parameters such as the previous cell arrival time, the bucket counter, and the cell interval time are required for the supervisory control. This leads to a problem of necessity of a memory having large capacity to keep such data.
It is therefore an object of the present invention to provide an apparatus for and a method of detecting an OAM cell for use with an ATM network including connections between one station and a plurality of stations in which the OAM cell is transferred at a transfer rate of one cell per second to thereby prevent the OAM cell from adversely influencing normal lines.
Another object of the present invention is to provide an apparatus for and a method of detecting an OAM cell for use with an ATM network including connections between one station and a plurality of stations in which even when a double failure occurs in the ATM network, one failed position can be determined and the memory to keep supervisory parameters needs only small capacity.
In accordance with the present invention, there is provided an OAM cell detecting apparatus for detecting an OAM cell in an ATM layer in an ATM network in which a station is connected to a plurality of stations. The apparatus includes OAM cell detecting means for detecting an OAM cell in an ATM layer, storage means connected to the OAM cell detecting means for keeping a timer counter value and failed state information for each virtual path or channel, timer incrementing means connected to the storage means for incrementing the timer counter value independently of a cell receiving period and for keeping, when the timer counter value exceeds a predetermined period of time equal to or less than one second, the timer counter value unchanged; timer counter comparing means connected to the OAM cell detecting means for comparing the timer counter value measuring a predetermined period of time equal to or less than one second after reception of the OAM cell with a reference value and for generating a discard signal only when the timer counter value is less than the reference value, failed state monitoring means connected to the OAM cell detecting means and the storage means for detecting the OAM cell for each virtual path or channel and for setting a failed state flag indicating failed state information of the storage means to xe2x80x9c1xe2x80x9d, and cell discarding means connected to the OAM cell detecting means, the storage means, the timer counter comparing means, and the failed state monitoring means for discarding, when the discard signal is received from the timer counter comparing means, the OAM cell from the OAM cell detecting means and for thereby generating an empty cell.
In accordance with the present invention, there is provided an OAM cell detecting apparatus for detecting an OAM cell in an ATM layer in an ATM network in which a station is connected to a plurality of stations. The apparatus includes OAM cell detecting means for detecting an OAM cell in an ATM layer, storage means connected to the OAM cell detecting means for keeping a failed state flag, failed state information, and failed position display change flag for each virtual path or channel, failed state monitoring means connected to the OAM cell detecting means and the storage means for detecting the OAM cell for each virtual path or channel and for setting a failed state flag indicating failed state information of the storage means to xe2x80x9c1xe2x80x9d, failed position display and comparator means connected to the OAM cell detecting means and the storage means, and cell discarding means connected to the OAM cell detecting means, the storage means, the failed state monitoring means, and the failed position display and comparator means for discarding, when the discard signal is received from the failed position display and comparator means, the OAM cell from the OAM cell detecting means and for thereby generating an empty cell. The failed position display and comparator means stores failed position display information included in the OAM cell in the storage means for each virtual path or channel. The failed position display and comparator means compares, when the failed position display change flag is xe2x80x9c0xe2x80x9d, failed position display information of the OAM cell from the OAM cell detecting means with failed position display information previously stored. The failed position display and comparator means generates, when the comparison results in mismatching, the discard signal and feeds the signal to the cell discarding means. The failed position display and comparator means compares, when the failed position display change flag of the storage means is set to xe2x80x9c1xe2x80x9d by externally controlled firmware or software, the failed position display information of the OAM cell from the OAM cell detecting means with the failed position display information previously stored, and does not generate a discard signal even when the comparison results in mismatching. The failed position display and comparator means then updates the failed position display information previously stored in the storage means to the failed position display information of the OAM cell from the OAM cell detecting means and sets the failed position display change flag to xe2x80x9c0xe2x80x9d.
In accordance with the present invention, there is provided an OAM cell detecting apparatus for detecting an OAM cell in an ATM layer in an ATM network in which a station is connected to a plurality of stations. The apparatus includes an OAM cell detecting means for detecting an OAM cell in an ATM layer, storage means connected to the OAM cell detecting means for keeping a timer counter value, a failed state flag, failed state information, and a failed position display change flag for each virtual path or channel, timer incrementing means connected to the storage means for incrementing the timer counter value independently of a cell receiving period and for keeping, when the timer counter value exceeds a predetermined period of time equal to or less than one second, the timer counter value unchanged, timer counter comparing means connected to the OAM cell detecting means for comparing the timer counter value measuring a predetermined period of time equal to or less than one second after reception of the OAM cell with a reference value and for generating a discard signal only when the timer counter value is less than the reference value, failed state monitoring means connected to the OAM cell detecting means and the storage means for detecting the OAM cell for each virtual path or channel and for setting a failed state (disabled state) flag indicating failed state information of the storage means to xe2x80x9c1xe2x80x9d, failed position display and comparator means connected to the OAM cell detecting means and the storage means, and cell discarding means connected to the OAM cell detecting means, the storage means, the timer counter comparing means, the failed state monitoring means, and the failed position display and comparator means for discarding, when the discard signal is received from the timer counter comparing means or the failed position display and comparator means, the OAM cell from the OAM cell detecting means and for thereby generating an empty cell. The failed position display and comparator means stores failed position display information included in the OAM cell in the storage means for each virtual path or channel. The failed position display and comparator means compares, when the failed position display change flag is xe2x80x9c0xe2x80x9d, failed position display information of the OAM cell from the OAM cell detecting means with failed position display information previously stored. The failed position display and comparator means generates, when the comparison results in mismatching, the discard signal and feeds the signal to the cell discarding means. The failed position display and comparator means compares, when the failed position display change flag of the storage means is set to xe2x80x9c1xe2x80x9d by externally controlled firmware or software, the failed position display information of the OAM cell from the OAM cell detecting means with the failed position display information previously stored, and does not generate a discard signal even when the comparison results in mismatching. The failed position display and comparator means updates the failed position display information previously stored in the storage means to the failed position display information of the OAM cell from the OAM cell detecting means and sets the failed position display change flag to xe2x80x9c0xe2x80x9d.
In accordance with the present invention, there is provided an OAM cell detecting method of detecting an OAM cell in an ATM layer in an ATM network in which a station is connected to a plurality of stations. The method includes the steps of detecting an OAM cell in an ATM layer by OAM cell detecting means, keeping a timer counter value and failed state information for each virtual path or channel by storage means; incrementing by timer incrementing means the timer counter value independently of a cell receiving period and keeping, when the timer counter value exceeds a predetermined period of time equal to or less than one second, the timer counter value unchanged, comparing by timer counter comparing means the timer counter value measuring a predetermined period of time equal to or less than one second after reception of the OAM cell with a reference value and generating a discard signal only when the timer counter value is less than the reference value, detecting the OAM cell for each virtual path or channel and setting a failed state flag indicating failed state information of the storage means to xe2x80x9c1xe2x80x9d by failed state monitoring means, and discarding, when the discard signal is received from the timer counter comparing means, the OAM cell from the OAM cell detecting means and for thereby generating an empty cell by cell discarding means.
In accordance with the present invention, there is provided an OAM cell detecting method of detecting an OAM cell in an ATM layer in an ATM network in which a station is connected to a plurality of stations. The method includes the steps of detecting an OAM cell in an ATM layer by OAM cell detecting means, keeping a failed state flag, failed state information, and a failed position display change flag for each virtual path or channel by storage means, detecting the OAM cell for each virtual path or channel and setting a failed state flag indicating failed state information of the storage means to xe2x80x9c1xe2x80x9d by failed state monitoring means, storing failed position display information included in the OAM cell for each virtual path or channel in the storage means by failed position display and comparator means, comparing by the failed position display and comparator means, when the failed position display change flag is xe2x80x9c0xe2x80x9d, failed position display information of the OAM cell from the OAM cell detecting means with failed position display information previously stored and generating, when the comparison results in mismatching, the discard signal and feeding the signal to the cell discarding means, comparing by the failed position display and comparator means, when the failed position display change flag of the storage means is set to xe2x80x9c1xe2x80x9d by externally controlled firmware or software, the failed position display information of the OAM cell from the OAM cell detecting means with the failed position display information previously stored, generating no discard signal even when the comparison results in mismatching, updating the failed position display information previously stored in the storage means to the failed position display information of the OAM cell from the OAM cell detecting means, and setting the failed position display change flag to xe2x80x9c0xe2x80x9d, and discarding by cell discarding means, when the discard signal is received from the failed position display and comparator means, the OAM cell from the OAM cell detecting means and for thereby generating an empty cell.
In accordance with the present invention, there is provided an OAM cell detecting method of detecting an OAM cell in an ATM layer in an ATM network in which a station is connected to a plurality of stations. The method includes the steps of detecting an OAM cell in an ATM layer by OAM cell detecting means, keeping a timer counter value, a failed state flag, failed state information, and a failed position display change flag for each virtual path or channel by storage means, incrementing by timer incrementing means the timer counter value independently of a cell receiving period and keeping, when the timer counter value exceeds a predetermined period of time equal to or less than one second, the timer counter value unchanged, comparing by timer counter comparing means the timer counter value measuring a predetermined period of time equal to or less than one second after reception of the OAM cell with a reference value and generating a discard signal only when the timer counter value is less than the reference value, detecting the OAM cell for each virtual path or channel and setting a failed state flag indicating failed state information of the storage means to xe2x80x9c1xe2x80x9d by failed state monitoring means, storing by the failed position display and comparator means failed position display information included in the OAM cell in the storage means for each virtual path or channel, comparing by the failed position display and comparator means, when the failed position display change flag is xe2x80x9c0xe2x80x9d, the failed position display information of the OAM cell from the OAM cell detecting means with the failed position display information previously stored, and generating, when the comparison results in mismatching, the discard signal and feeding the signal to the cell discarding means, comparing by the failed position display and comparator means, when the failed position display change flag of the storage means is set to xe2x80x9c1xe2x80x9d by externally controlled firmware or software, the failed position display information of the OAM cell from the OAM cell detecting means with the failed position display information previously stored, and generating no discard signal even when the comparison results in mismatching, updating the failed position display information previously stored in the storage means to the failed position display information of the OAM cell from the OAM cell detecting means, and setting the failed position display change flag to xe2x80x9c0xe2x80x9d, and discarding by cell discarding means, when the discard signal is received from the timer counter comparing means or the failed position display and comparator means, the OAM cell from the OAM cell detecting means and thereby generating an empty cell.